NAME
Coro::ProcessPool - an asynchronous process pool
SYNOPSIS
use Coro::ProcessPool;
my $pool = Coro::ProcessPool->new(
max_procs => 4,
max_reqs => 100,
);
my $double = sub { $_[0] * 2 };
# Process in sequence
my %result;
foreach my $i (1 .. 1000) {
$result{$i} = $pool->process($double, [$i]);
}
# Process as a batch
my @results = $pool->map($double, 1 .. 1000);
# Defer waiting for result
my %deferred = map { $_ => $pool->defer($double, [$_]) } 1 .. 1000);
foreach my $i (keys %deferred) {
print "$i = " . $deferred{$i}->() . "\n";
}
$pool->shutdown;
DESCRIPTION
Processes tasks using a pool of external Perl processes.
METHODS
new
Creates a new process pool. Processes will be spawned as needed.
max_procs
This is the maximum number of child processes to maintain. If all
processes are busy handling tasks, further calls to "process" in .
will yield until a process becomes available. If not specified,
defaults to the number of CPUs on the system.
max_reqs
If this is a positive number (defaults to 0), child processes will
be terminated and replaced after handling "max_reqs" tasks. Choosing
the correct value for "max_reqs" is a tradeoff between the need to
clear memory leaks in the child process and the time it takes to
spawn a new process and import any packages used by client code.
process($f, $args, $timeout)
Processes code ref $f in a child process from the pool. If $args is
provided, it is an array ref of arguments that will be passed to $f.
Returns the result of calling "$f-"(@$args)>.
This call will yield until the results become available. If all
processes are busy, this method will block until one becomes available.
Processes are spawned as needed, up to "max_procs", from this method.
Also note that the use of "max_reqs" can cause this method to yield
while a new process is spawned.
A timeout may be optionally specified in fractional seconds. If
specified, $timeout will cause "process" to croak if $timeout seconds
pass an no process becomes available to handle the task.
Note that the timeout only applies to the time it takes to acquire an
available process. It does not watch the time it takes to perform the
task.
map($f, @args)
Applies $f to each value in @args in turn and returns a list of the
results. Although the order in which each argument is processed is not
guaranteed, the results are guaranteed to be in the same order as @args,
even if the result of calling $f returns a list itself (in which case,
the results of that calcuation is flattened into the list returned by
"map".
defer($f, $args)
Similar to "process" in ., but returns immediately. The return value is
a code reference that, when called, returns the results of calling
"$f-"(@$args)>.
my $deferred = $pool->defer($coderef, [ $x, $y, $z ]);
my $result = $deferred->();
shutdown
Shuts down all processes and resets state on the process pool. After
calling this method, the pool is effectively in a new state and may be
used normally.
A NOTE ABOUT IMPORTS AND CLOSURES
Code refs are serialized using Storable to pass them to the worker
processes. Once deserialized in the pool process, these functions can no
longer see the stack as it is in the parent process. Therefore, imports
and variables external to the function are unavailable.
Something like this will not work:
use Foo;
my $foo = Foo->new();
my $result = $pool->process(sub {
return $foo->bar; # $foo not found
});
Nor will this:
use Foo;
my $result = $pool->process(sub {
my $foo = Foo->new; # Foo not found
return $foo->bar;
});
The correct way to do this is to import from within the function:
my $result = $pool->process(sub {
use Foo;
my $foo = Foo->new();
return $foo->bar;
});
...or to pass in external variables that are needed by the function:
use Foo;
my $foo = Foo->new();
my $result = $pool->process(sub { $_[0]->bar }, [ $foo ]);
COMPATIBILITY
"Coro::ProcessPool" will likely break on Win32 due to missing support
for non-blocking file descriptors (Win32 can only call "select" and
"poll" on actual network sockets). Without rewriting this as a network
server, which would impact performance and be really annoying, it is
likely this module will not support Win32 in the near future.
The following modules will get you started if you wish to explore a
synchronous process pool on Windows:
Win32::Process
Win32::IPC
Win32::Pipe
AUTHOR
Jeff Ober
LICENSE
BSD License